The ends of crankshafts for automotive vehicles, for example, for passenger cars, are usually machined in machines specifically designed for performing the corresponding operations. For example, the crankshafts can be arranged in a workstation located between two machining modules (each can be configured to simultaneously machine a plurality of crankshafts, generally using a tool for each crankshaft, for example, using a multi-spindle head), such that a first machining module machines one end of the crankshaft (or one end of several crankshafts) and the other machining module simultaneously machines the other end of the crankshaft (or of the crankshafts).
To achieve a high production rate and an efficient use of the machinery, it is desirable for both machining modules to work with a high performance and with a minimum downtime between operations. WO-A-2009/103825 describes an example of how to achieve the reduction of the downtime between operations in a machine for machining crankshafts.
As described in WO-A-2009/103825, it is usual for crankshafts to have two different ends, a first end which will hereinafter be referred to as “flange end” and a second end which will hereinafter be referred to as “post end”. Both ends require different machining operations, whereby it is usual for the machining of one of said ends to require more time than the machining of the opposite end; it is usual for the flange end to require a substantially greater machining time than the post end, as explained in WO-A-2009/103825. In the present document, the terms “flange end” and “post end” must not be interpreted in a limiting manner, as if they refer to a specific design of the crankshafts, but rather they are used in a general manner to distinguish between two ends of a crankshaft which require different machining operations.
The solution in WO-A-2009/103825 is based on the use of two workstations, in one of which the crankshafts are arranged in a reverse manner (i.e., “rotated” 180 degrees) with respect to the crankshafts of the other one. In a described embodiment, the workstations are located between two machining module bedplates or guides, on which respective machining modules move. A first machining module can thus machine the flange ends of the crankshafts of the first workstation, to then move laterally to the second workstation to machine the post ends of the crankshafts in the second workstation. In a reverse manner, the second machining module can start by machining the post ends of the crankshafts in the first workstation, to then move to the second workstation to machine the flange ends of the crankshafts located in said second workstation. Therefore, if the time for machining the flange ends requires a time X and the machining of the post ends requires a time Y (which can many times be substantially less than X, for example, a quarter of X), the first machining module can conclude the machining work in both workstations after an approximate time of X+Y (without counting movement times, etc.), and the second machining module can conclude the machining work in both stations after a time Y+X. In other words, the cycle time can be approximately X+Y (without counting movements, delays due to loading and unloading, etc.), and during this time both machining modules can be in full performance, without any of them having to wait for a substantial time for the other one to finish its machining operation. A rather short cycle time and a good exploitation of the machinery are thus achieved.
Nevertheless, and despite the fact that the machine and method described in WO-A-2009/103825 can work satisfactorily from many points of view, they can have several limitations. For example, it may be difficult to perform the loading and unloading in the two workstations from one and the same loading and unloading point or station. Another possible limitation is that in the event of a breakdown in one of the machining modules, the machine does not allow machining both ends of the crankshafts. Another possible limitation is that it may be difficult to perform certain machining operations, which require a determined working angle between the tool-head and the crankshaft (for example, the machining of the keyway or of lightening holes), without using additional machining modules or tool-head changes.